Fix a crash when double-clicking a replay with an unknown map.
Merge pull request #6800 from pchote/fix-replay-browser

Fix a crash when double-clicking a replay with an unknown map.
Made gdi04c easier to win and added cell trigger guards
Move Utils.Seconds and .Minutes into DateTime global

Also renames Date.IsHalloween to DateTime.IsHalloween
Move Utils.CenterOfCell into Map global
Point out pitfalls in the Lua API documentation
Whitespace fixes
Remove more references to old Lua API

Fixes #6811